Tech Talk - Sweep Rate

(603) 226-DYNO

Read tips on selecting the optimum automated test sweep rate for evaluating an engine's real world performance on the dynamometer.

"Reprinted from the DYNOmite Summer - 2004 Newsletter article."

Dyno Tech Talk is a compilation or copyrighted material, however, relevant web sites and forums are welcome to link to the Dyno Tech Talk index page.

How do I select the best Sweep Rate?

Selecting the best Sweep Rate... is an important step in dynoing to better drag engine performance. When utilizing the DYNOmite's Automated Load Control Servo, in conjunction with DYNO-MAX 2000 “Pro’s”Auto Test Wizards, you can select from a wide array of Sweep Rates and test behaviors. So, what's the right choice?

In most cases, the simple linear sweep rate (i.e. 200 RPM/second) is not the best selection for evaluating real world engine acceleration performance! Vehicles actually accelerate (under WOT) along a non-linear (falling) curve. Any constant sweep rate test runs an engine too long at low RPM - and too little at high RPM. If you graph and sum average test power (area under the curve) for such a pull, you're allowing way too much credit in its earliest range - utilized only briefly out on a track.

Although many dynamometer pulls get run this way, they're providing a relatively poor simulation of the engine's real world full throttle acceleration Time vs. RPM curve. Worse still are pure inertia dynos - which, unfortunately, have an increasing rate of acceleration near the end of the run (due to engine power building with RPM)!

The solution? Use the Auto Test wizard’s Exponential Sweep Rate toggle. It generates a decreasing curve - where the engine spends appropriately more test time at its higher RPM’s. For such tests, the RPM/sec selection merely sets the average rate - so you can control the test's duration. (Note: The Drag, Road Course, and Simulate Road Load tests also accelerate slower as speed builds).

Try evaluating your next round of tuning experiments this way. Once you've captured a series of these (more relevant) pulls, compare their Average Hp. Use Graph Set Up to overlay each run. Then, check the “Show Averages” box. That'll return an average summation Hp number (on the Data Points Listing) which truly indicates how each combination will stack up in a real world acceleration battle!